Thread: Exhaust flue too close to window?

Tankless water heater in garage with combination exhaust flue and supply air vent to the exterior. The distance between the flue/supply is 36 inches to the window.

I am thinking this has got to be a high efficiency device to use PVC exhaust so the the exhaust is cool. But that does not make it any less deadly.

Wadda ya think? Too close?

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Looks like IRC 2427.8 indicates minimum of 12" for >50k Btu. Less distance for lower Btu direct vent gas appliances.

Bruce,the gases at any temp is still dangerous altough it it appears to be not under the window but away 3 feet in your post should be ok.

Check the manufacturer instructions. It should specify clearances to the window.

That water heater needs protection from vehicle impact, no?

Good morning, Gents:

I don’t no nuthin’ ‘bout building codes….

But I do know something about contaminant migration, and I can definitely say that from an industrial hygiene perspective, the terminus is inappropriate, and contaminants will reenter the house, and human exposures to the exhaust gases will occur.

The reason is due to a number of factors including:
1) Exhausting into building envelope (Industrial Hygienists use a different definition of “building envelope” than Home Inspectors)
2) Proximity to the window
3) Location in a corner
4) Positive pressure vent stack in occupied space

Now, I know that you guys like codes, so: According to the ANSI/ASHRAE Standard 62.1-2007, (Ventilation for Acceptable Indoor Quality), the location of the vent in the photo would violate the provisions of Sections 5.3 and 5.6.1 (which would require at least 15 feet between the terminal and the window); and it could be legitimately argued that the Standard, in its strictest interpretation, would require 30 feet separation.

However, standards notwithstanding, the vent is too close and it is positively pressurized along the length of the duct – both spell “human exposure.”

Cheers!
Caoimhín P. Connell
Forensic Industrial Hygienist
Forensic Industrial Hygiene


(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)

AMDG

Always verify with the manu8facturer's instructions but....I think the concept is that since it is a direct vent with its own combustion air supply, the exhaust is clean and does not contain appreciable amounts of CO.

Good afternoon, Dana:

Your comment about the CO may well be correct – however, CO is not the only combustion byproduct of concern. Instead, we are still concerned about NOx, thiols, mercaptans, CO2 and of course moisture. Most important of all, we also know that gas appliances can exhaust massive quantities of ultrafine particles.

Finally, I have evaluated many gas appliances, which, according to the manufacturer, should not produce “appreciable� concentrations of CO only to find that they in fact do produce toxicologically significant quantities.

So, using the ANSI/ASHRAE standard the exhaust stack is too close andthe location should be remediated. By the way, the ANSI/ASHRAE standard is not a professional standard, rather it is a national consensus standard, and as such, may already be incorporated by reference in the local building code.

Cheers!
CaoimhÃ*n P. Connell
Forensic Industrial Hygienist
Forensic Industrial Hygiene

P.S. - I love the tag-line!

(The opinions expressed here are exclusively my personal opinions and do not necessarily reflect my professional opinion, opinion of my employer, agency, peers, or professional affiliates. The above post is for information only and does not reflect professional advice and is not intended to supercede the professional advice of others.)

AMDG